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Avoid user-not-found timing attacks w/ dummy hash #15

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Merged
cognifloyd merged 2 commits into from
Sep 13, 2025
Merged

Avoid user-not-found timing attacks w/ dummy hash #15

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9389260
Avoid user-not-found timing attacks w/ dummy hash
cognifloyd Sep 13, 2025
b58759a
make pw var available when user not found
cognifloyd Sep 13, 2025
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10 changes: 7 additions & 3 deletions st2auth_flat_file_backend/flat_file.py
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,9 @@

LOG = logging.getLogger(__name__)

# dummy pw is "testpassword" (used when user not found to avoid timing attacks)
DUMMY_HASH_DATA = "$2y$05$Vhvhbk0SYN3ncn9BSvXEHunzztBWfrwqOpX1D0GhrFvM1TcADpKoO"


class HtpasswdFile(object):
"""
Expand Down Expand Up @@ -71,10 +74,10 @@ def _load_file(self):
self.entries[username] = hash_data

def check_password(self, username, password):
encode_local = locale.getpreferredencoding()
pw = bytes(password, encoding=encode_local)
if username in self.entries:
hash_data = self.entries[username]
encode_local = locale.getpreferredencoding()
pw = bytes(password, encoding=encode_local)
if hash_data.startswith("$apr1$"):
LOG.warning(
"%s uses MD5 algorithm to hash the password."
Expand Down Expand Up @@ -103,7 +106,8 @@ def check_password(self, username, password):
)
return compare_hash(crypt.crypt(password, hash_data), hash_data)
else:
# User not found.
# User not found. Do a dummy hash to avoid timing attacks.
_ = bcrypt.checkpw(pw, bytes(DUMMY_HASH_DATA, encoding=encode_local))
return None


Expand Down